1. Field of the Invention
The present invention concerns combustion devices and more particularly a method and apparatus for pretreating hydrocarbon fuel to achieve an activated condition to reduce delays in ignition and combustion of the fuel upon injection into the combustion chamber of a combustion device.
2. Description of the Prior Art
It has heretofore been proposed to achieve so called "hypergolic" combustion, particularly of hydrocarbon fuels in an internal combustion engine, such that ignition delay and the time required to complete combustion are both negligible after the fuel is introduced into an oxidizing atmosphere.
For a detailed discussion, see U.S. Pat. No. 4,448,176; SAE paper no. 850089 "Hypergolic Combustion in an Internal Combustion Engine"; and, SAE paper 820356, "The Influence of Initial Fuel Temperature on Ignition Delay"; each of which are incorporated herein by reference.
Hypergolic combustion has a number of advantages, as detailed in the aforementioned references, particularly in the context of internal combustion reciprocating engines.
As also detailed in the aforementioned references, ignition delay is believed to occur due to the need for the fuel molecules to first be disassociated into radicals in order to combine with oxygen molecules, which themselves must be disassociated for oxidation to occur. In a typical combustion process, an ignition device such as a spark plug causes a localized increased concentration of fuel radicals in a fuel-air mixture, sufficient for initiation of combustion. The release of heat from that localized combustion in turn causes additional disassociation of adjacent fuel molecules to enable combustion to propagate through the entire charge of fuel-air mixture.
As discussed in the aforementioned U.S. Pat. No. 4,448,176, if there is a pretreatment of the fuel such as to cause a disassociation of a critical proportion of molecules in each quantity of fuel, much higher than the proportion occurring at ambient temperatures, there is an "activation" of the fuel yielding substantially instantaneous ignition and combustion.
In order that such an increased, critical proportion of fuel molecules be disassociated into radicals, energy must be expended to bring this proportion of the fuel molecules to the relatively high energy state corresponding to the disassociated condition of the fuel molecules.
As described in the aforementioned U.S. Pat. No. 4,448,176, if fuel is heated to relatively elevated temperatures in excess of 1000 F..degree., this causes such critical proportion of fuel molecules to be disassociated to form radicals, since such proportion of the fuel molecules is thereby brought to a high energy state.
A disadvantage of preheating of the fuel is the tendency for cracking of the fuel molecules at high temperatures, and the resultant formation of coke, tending to clog the fuel flow passages.
In co-pending application Ser. No. 813,882 filed on Dec. 26, 1986, attorney docket no. 85 ERC 271, now U.S. Pat. No. 4,651,703, there is described a method and system for heating of the fuel to elevated temperatures by partial combustion of the fuel prior to being injected into the combustion chamber. This process is able to heat the fuel to such sufficiently elevated temperatures, that upon injection into the combustion chamber hypergolic combustion will result.
Alternatively, catalysis is utilized to augment the effect of heating to achieve fuel activation.
In SAE paper 800264 entitled "Gasification of Diesel Fuel for a Low Emission, High Efficiency Engine System"; in Siemens Forsch.-u. Entwickl.-Ber. Bd. 6 (1977) Nr. 5, entitled "Autothermal Gasification of Liquid Hydrocarbons by Partial Oxidation"; and Siemens Forsch.-u. Entwickl.-Ber. Bd. 7 (1978) Nr. 2 entitled "Compact Gas Generator for Fuel Gasification Aboard Motor Vehicles" each of which is hereby incorporated by reference, there is disclosed a method of gasifying liquid hydrocarbon fuels.
This method also involves partial oxidation of the fuel in the presence of a catalyst to form a high temperature gas, rich in hydrogen and hydrocarbon radicals. This gas is described as being useable as a fuel for an internal combustion engine if it is cooled to room temperature and mixed with air as in a conventional spark ignited engine.
It is desirable in using partial combustion to preheat the fuel to limit the degree of combustion to that strictly necessary to achieve the desired level of formation of radicals so as to not expend an undue proportion of the heat energy of the fuel in pretreatment.
It is also desirable to limit the temperature of the product gas to minimize the formation of coke which tends to clog the various flow passages.
Partial combustion by means of a catalytic reaction is highly desirable to accomplish these ends, since such combustion in the presence of a catalyst tends to produce a high proportion of radicals, and such combustion can be initiated and will proceed at much lower temperatures. This allows the elimination of an ignition device to initiate the partial combustion process.
The partial combustion process itself may be more precisely controlled by the use of a particular catalyst material and using a preselected catalyst morphology.
Accordingly, it is an object of the present invention to provide an apparatus and method of pretreating fuel to achieve a high proportion of radical formation such as to enable hypergolic combustion by catalytic partial combustion of vaporized fuel which optimizes the catalytic effect such as to eliminate or substantially alleviate the tendency for coke formation and allowing catalytic ignition of the fuel in the pretreatment phase.